Automatic cutoff for transformers



March 8, 1949.

R. H. SEAMAN AU'I'QMATIC CUTOFF FOR TRANSFORMERS Filed Sept. 25, 1945Bic/7 arc! +1 .5 50277027- Wm M Patented Mar. 8, 1949 AUTOMATIC CUTOFFFOR TRANSFORMERS Richard H. Seaman, Los Angcles, Calif., assignor toMega Corporation, Los Angeles, Calif., a corporation of CaliforniaApplication September 25, 1945, Serial No. 618,536

2 Claims. I

This invention relates to the provision of means to. protect electricaltransformers of the step-up type from injury in the event that thesecondary circuit of the transformer becomes accidentally opened.

The invention is hereinafter described as particularly applied totransformers used in neon sign work, although the scope of the inventionis evidently not necessarily so limited.

Transformers used in gaseous discharge tube circuits, and particularlyin connection with neon tube signs, are of the high voltage type, thesecondary voltage being usually of the order of 10,000 to 15,000 volts.Although it is general practice to provide tarnsformers of the highleakage type for such use, the accidental breaking of the sign, which isa common occurrence, will nevertheless cause high voltages to build upin the secondary Winding of the transformer with the result that if thecircuit is not promptly disconnected the transformer will probablybecome overheated and ruined.

Because of the danger of fire due to shorting of the high tension wiringof the sign caused by accidents or damage by storms which may possiblyoccur in view of the exposed positions in which illuminated signs areoften necessarily placed, it is advantageous to provide protectivedevices for such signs which will act practically instantaneously tointerrupt the electrical power supply to the transformer; such devices,for maximum safety, should operate if either side of the high tensioncircuit becomes open or accidentally grounded.

Also since it is frequently necessary to replace gaseous discharge tubesand such replacement may be attempted by unskilled persons, particularlyin indoor installations in which gaseous discharge tubes are likely tobe of the hot cathode high current type, serious injury from electricalshock may be experienced by contacting the socket terminals with thefingers if the person attempts to fit a new tube in the sockets withoutfirst turning ofi the current. By the use of the device of thisinvention the current is cut off from the tube circuits as soon as thesecondary or high voltage circuit is interrupted either by breaking ofthe tube or removal thereof from the socket without first turning 01fthe current so that electric shocks cannot be experienced.

The peak voltages used in neon sign work is necessarily high in order tosecure the striking voltage of the tube, which may be 25% or more inexcess of the normal operating voltage. The brief application of suchvoltage in the transformer 2 previous to the lighting of the sign doesnot harm the transformer since the voltage drops immediately the sign islighted, but the generation of this high voltage for any considerableperiod of time, should the sign be broken, will damage the transformer.

Neon signs are very commonly erected on the roadside or in relativelyinaccessible places, such as on roof tops and the like, and aconsiderable period of time may elapse before the sign is visited formaintenance or the inoperativeness of the sign is noticed. Large numbersof transformers are used in connection with such gaseous discharge tubesigns, both because of the great number of such signs and because largesigns are commonly built up of separate sections, each provided with itsown transformer, so that the cost of replacement of damaged transformersconstitutes a relatively heavy item in the maintenance of such signs.

It is an object of the invention to protect transformers, particularlyof the high voltage type used with gaseous discharge tubes, such as neonsigns, by the provision of an inexpensive device which will act tointerrupt the primary circuit of the transformer should the secondarycircuit he accidentally opened.

It is a further object of the invention to provide a device of the kinddescribed which is simple in construction and inexpensive tomanufacture.

A further object of the invention is to provide a device of the kinddescribed which may very readily be renewed or reset when the sign hasbeen repaired.

A further object of the invention is to afford safety in the repairingof neon and the like signs by automatically disconnecting the tubesockets of the sign from the source of high voltage.

A further object of the invention is to provide a method of protectingtransformers from damage due to building up of excessively high voltagein the secondary winding thereof.

Further features and objects of the invention will hereinafter appear inthe following description taken in conjunction with the accompanyingdrawings, in which:

Fig. l is a diagram showing a neon sign having the transformer providedwith the safety device of the invention;

Fig. 2 is a section through one form of the safety device;

Fig. 3 is a section through a safety device of a; modified form in whichthe device is capable of being reset after each operation thereof;

Fig. 4 is a plan view of the device diagrammatically shown in Fig. 1formed as a tubular fuse; and

Fig. 5 is a section through another form of the invention in which twoof the devices shown in Fig. 2 are combined in a single unit.

Referring now to Fig. 1, a neon sign is indicated by the numeral ID. Thesign is supplied with electric current from power lines l2 by means of ahigh leakage transformer 14, the primary winding being indicated at I6and the secondary winding at IS. The protective device is furnished withthree leads 22 and 24, which are connected in the supply line, and 26,which is connected to the secondary winding.

The protective device shown in detail in Fig. 2 comprises a fuse socket28 provided with terminals 30 and 32 to which the leads 22 and 24 areconnected in the usual manner, the lead 22 connecting with the metalshell of the socket and the lead 24 connected with a central contact 34.The socket may be connected in the power line by the terminals 3|] and32. A fuse plug 3% provided with a fusible element 38 of appropriatecapacity is screwed into the fuse socket. A tubular member 40 is screwedor otherwise inserted into the fuse plug. The conductor 26 connected tothe secondary of the transformers is sealed into one end of the tubularmember and terminates in a hook 4| spaced above fusible element 38 toconstitute a spark gap.

Should the secondary circuit be accidentally opened, as by breaking ofthe neon tube, and the voltage in the secondary therefore start to buildup, an arc will be established between the end 4| of conductor 26 andthe fusible element 38, which.

will rapidly cause melting of the fusible element and thereforeinterruption of the primary circuit of the transformer.

After repair work on or replacement of the neon tube it is necessary toinsert a new fuseplug in the fuse socket, which may be furnished withthe cylindrical element 40, in which case of course the conductor 26 ofthe burned fuse element would have to be disconnected and the conductor26 of the new element connected in its place, or the tubular elementmight be merely pulled out of or unscrewed from the burned fuse plug andinserted or screwed into the new plug.

In the form of the device shown in Fig. 3, the fusible element of theform of the device shown in Fig. 2 is replaced by a bimetallic strip 42but the cylindrical element 40 may be formed as in the device previouslydescribed. The form of the device shown in Fig. 3 is designed forpermanent installation and comprises a socket 44 provided with aterminal 48 connected to the bimetallic element and with a terminal 48connected to a pivoted contact piece 50. The device may be connected inthe primary circuit of the transformer by interrupting the line l2,connecting one terminal to the line at one side of the gap and the otherterminal to the line at the other side of the gap.

The bimetallic element 42 is shown as bent into a curve against theinner side of which the pivoted contact piece 50 bears, byreason of theforce exerted by compression spring 52 arranged between a button 54 andthe outside surface of the socket 44. The button 54 is mounted at oneend of a strip of insulating material 56 pivoted to the pivoted contactpiece 50. In this construction, when arcing occurs between the end ofconductor 26. and the bimetallic element 42, the heat generated willcause the bimetallic element to move out of contact with the pivotedcontact piece 50,

which will be pulled forwardly by spring 52, thus interrupting andmaintaining the interruption of the primary circuit.

Cooling of the bimetallic strip 42 will cause it to return to itsoriginal position and after the gaseous discharge tube has been repairedor replaced the contact piece 56 may be brought to its original positionby pushing in the stud 54.

It will be noted that the end of the bimetallic strip is shown as curvedin such a manner as to enable the contact piece to flex the stripsuiiiciently to slip into position.

In the form of the invention shown in Fig. 4, the device is constructedin the form of a cylindrical fuse which may be inserted in clips mountedin the transformer housing, the leads 22 and 24 being connected in theprimary circuit of the transformer and the lead 26 connected to thesecondary winding of the transformer.

In order to be sure that the primary circuit will be broken, no matterhow the secondary circuit is interrupted, it may be advisable to mountthe device of the invention in both sides of the secondary circuit. Theform of the invention shown in Fig. 5 is designed to enable this to bedone with a single device instead of using two separate devices.

The fusible element 60 in Fig. 5 is arranged as in the form of theinvention shown in Fig. 2 and is similarly connected in the primarycircuit of the transformer but the device provides a spark gap for eachside of the secondary circuit formed by conductors 62 and 64, eachconnected to one side of the secondary circuit and spaced from thefusible element 60.

While the device in all forms operates satisfactorily when the sparkgaps are in air, the operation of the device may be speeded up to bepractically instantaneous by positioning the elements in a tubeevacuated of air and containing oxygen. While the fusible element ismade of magnesium, in such a construction the first starting of thespark will of course immediately fuse the element Gil. It will beobvious that other gases vigorously supporting combustion may be used,and that fusible elements may be made from other readily fusible butconductive materials.

It is pointed out that by the use of the device of the invention, theinterruption of the primary circuit is positive and the sockets for thetubes are therefore free of high voltage, facilitating Work on the sign.

The device of the invention is of great utility in that it enables thepresent relatively high expense of replacing damaged transformers to beavoided, and also because it avoids serious electrical shocks to workmenengaged in the moving,

with an electrical circuit including a step-up transformer having aprimary circuit and a sec-' ondary circuit, and a gaseous dischargetube'in said secondary circuit, comprising a base having a pair ofterminals adapted to be connected in series with the primary circuit ofsaid' transformer, and formed to provide'a socket, a hollow fuse bodymounted in the socket of said base.- a"

readily fusible conductor in said body, cooperating conductive means onsaid base and'saidbody establishing electrical connection between theterminals of said base and the respective ends of said fusibleconductor, and an arcing terminal mounted in said body with its innerend forming an arc gap with said fusible conductor, said arcing terminalbeing adapted to be connected to one side of said secondary circuit,said fusible conductor and said arcing terminal being enclosed withinsaid fuse body.

2. A protective device for use in combination with an electrical circuitincluding a step-up transformer having a primary circuit and a secondarycircuit, and a gaseous discharge tube in said secondary circuit,comprising a base having a pair of terminals adapted to be connected inseries with the primary circuit of said transformer, and formed toprovide a socket, a hollow fuse body detachably mounted in the socket ofsaid base, a readily fusible conductor in said body, cooperatingconductive means on said base and said body establishing electricalconnection between the terminals of said base and the re- REFERENCESCITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,848,152 Bieger Mar. 8, 1932 201,859,377 Boudion May 24, 1932 2,099,500 Sanders Nov. 16, 1937

